Lithium ion (Li-ion) cells have been widely used for power and energy applications. Heat generation within Li-ion cells causes problems for performance, longevity, and safety, especially for those power cells required to be continuously discharged at extremely high currents. It may not be a significant issue for individual cells operated in ambient air even when they are discharged at their highest allowable currents. However, the issue can be severe when the cells are discharged in an assembled battery pack. In a battery pack, a cell is surrounded by neighboring cells, which are also generating heat. In the space-limited pack, cell cooling becomes difficult. If effective cooling is not available, the cells have to be derated to a much lower operation current to ensure safe operations. For example, cells that are rated for 500 A in ambient conditions can only be discharged at 200 A in a battery pack of twelve cells due to the heat generation inside the pack. The derating of discharge current will result in more paralleled battery pack series to reach the targeted currents. Moreover, the poor heat transfer within the battery pack will also increase cool-down time and reduce the cycle frequency.
WO 2015/123676 by IntraMicron describes a battery pack made of microfibrous media (MFM) filled with phase change materials (PCM), i.e. MFM-PCM. The MFM is a sintered 3D network made of micron-sized metal fibers. It typically has a high void volume of 70-99.5 vol %. For heat transfer purposes, the fibers are made of thermally conductive metals such as copper, nickel, aluminum, and their alloys and have a fiber diameter less than 100 microns. PCM are commonly paraffin waxes, glycols, fatty acids, inorganic hydrated salts, eutectic alloys, etc. IntraMicron's approach demonstrated superior thermal management performance compared with the traditional cooling tube approach.
It is an object of the invention to provide battery packs that are able to efficiently dissipate heat from multiple cells in the pack.